R语言程序 自写函数 init.igraph报错

根据《R语言与网站分析》第九章中的一个程序 init.igraph 写的，与原文无误，但运行还是报错 数据我已经放进去了，执行init.igraph就报错

library(igraph)
from<-c("a","a","a","a","a","b","b","b","c","c","c","d","d","d","e","e","f","f")
to<-c("d","c","b","e","f","c","d","a","d","a","b","a","c","b","a","f","e","a")
data<-data.frame(from=from,to=to)

init.igraph<-function(data,dir=F,rem.multi=T){
labels<-union(unique(data[,1]),unique(data[,2]))
ids<-1:length(labels)
from<-as.character(data[,1]);
to<-as.character(data[,2])
edges<-matrix(c(ids[from],ids[to]),nc=2)
g<-graph.empty(directed=F)
g<-add.vertices(g,length(labels))
V(g)$label=labels
g<-add.edges(g,t(edges))
if(rem.multi){
E(g)$weight<-count.multiple(g)
g<-simplify(g,remove.multiple=TRUE,remove.loops=TRUE,edge.attr.comb="mean")

}
g
}

https://blog.csdn.net/sinat_26917383/article/details/51436643